A major problem in the design and manufacture of investment cast metal woods is the requirement the head weight be maintained between 195 to 208 grams depending on the weight of the attached shaft assembly. This weight range is necessary to yield swing weights in the range of C-9 to D-3.
To approach this weight range in stainless steel or other similar specific gravity metals it is necessary to cast the face wall no greater than 0.125 inches and the perimeter walls averaging no more than about 0.040 inches. This is no small task. For the perimeter walls to average 0.040 inches, the inherent inaccuracies in investment casting dictate that the perimeter wall in spots diminish to 0.020 inches or less. Since the head must be ground and polished after casting and since many areas of the head have artwork, graphics and text on the order of 0.010 to 0.018 inches in depth, the 0.020 inch minimum wall thickness is in many cases unacceptably too thin, resulting in part rejection or subsequent wall failure.
To ameliorate this problem reinforcing techniques have been developed for the forward wall that permit the forward wall to be made lighter and the perimeter walls heavier to not only eliminate the manufacturing problem of excessively thin outer walls but also to enhance the perimeter weighting of the head.
The landmark contribution to this technology is found in the Raymont, U.S. Pat. No. 3,847,399, assigned to the assignee of the present invention. Mr. Raymont discovered that by providing a honeycomb structure behind the forward wall, perimeter weighting was enhanced and a lighter and reinforced face could be produced.
In the Allen, U.S. Pat. No. 4,930,781, also assigned to the assignee of the present invention, a similar honeycomb reinforcement is used in an investment cast metal wood to rigidify the face to reduce face deflection so a more uniform deflection pattern could be achieved across the face.
The object of the present invention is to enlarge the sweetspot on the club face, not just by increasing perimeter weighting although such exists, by enlarging the club face area.
I have found that by increasing the total area of the face wall that the sweetspot area on the face increases at a rate far greater than the increase in overall face area.
Partitionings in golf club heads for various reasons are shown in the Marker, U.S. Pat. No. 1,592,463; the Tobia, U.S. Pat. No. 1,658,581; the Drevitson, U.S. Pat. No. 1,678,637; the Schaffer, U.S. Pat. No. 2,460,435; the Curley, U.S. Pat. No. 2,592,013; the Mader, U.S. Pat. No. 4,021,047; the Nygren, U.S. Pat. No. 4,076,254; the Zebelean, U.S. Pat. No. 4,214,754; the Motomiya, U.S. Pat. No. 4,438,931; the Hayashi, et al., U.S. Pat. No. 4,449,707; the Yamada, U.S. Pat. No. 4,535,990; the Teramoto, et al., U.S. Pat. No. 4,645,207; the Straza, et al., U.S. Pat. No. 4,679,792; the Chen, et al., U.S. Pat. No. 4,681,321, and the Tilley, U.S. Pat. No. 4,730,830. There have also been attempts to provide club heads with rear covers, such as shown in the Nero, U.S. Pat. No. 1,825,244, and the Carlino, U.S. Pat. No. 3,637,218, but these attempts have not been applied to thin walled investment cast club heads, and are thus not directed to any of the problems in that casting art.
It is a primary object of the present invention to provide a metal wood with a larger sweetspot by enlarging the face wall area without increasing head weight or sacrificing head strength.